Leuprolide acetate is an LHRH agonist analog that is useful in the palliative treatment of hormonal related prostate cancer, mammary cancer, endometriosis, and precocious puberty. With continued use, leoprolide acetate causes pituitary desnsitizing and down-regulation to affect the pituitary-gonodal axis, leading to suppressed circulating levels of luteinizing and sex hormones. In patients with advanced prostate cancer, achieving circulating testosterone levels of less than or equal to 0.5 ng/ml (chemical castration level) is a desired pharmacological indicator of therapeutic action.
Originally, leuprolide acetate was launched in the United States as a daily subcutaneous (s.c.) injection of the analog solution. The inconvenience of chronic repetitive injections was later eliminated by the development of a one month sustained release depot product based on poly(DL-lactide-co-glycolide) microspheres (Lupron® Depot). Currently, one, three, and four month formulations are widely available as intramuscular (i.m.) injections of microspheres.
Although the current Lupron® Depot microspheres appear to be effective, the microsphere products are difficult to manufacture, and they all require a deep intramuscular (i.m.) injection using large volumes of fluid to ensure that all of the microspheres are properly administered to the patient. These injections are often painful and lead to tissue damage.
Biodegradable polymers other than Lupron® Depot have been employed in many medical applications, including drug delivery devices. The drug is generally incorporated into the polymeric composition and formed into the desired shape outside the body. This solid implant is then typically inserted into the body of a human, animal, bird, and the like through an incision. Alternatively, small discrete particles composed of these polymers can be injected into the body by a syringe. Preferably, however, certain of these polymers can be injected via syringe as a liquid polymeric composition.
Liquid polymeric compositions useful for biodegradable controlled release drug delivery systems are described, e.g., in U.S. Pat. Nos. 4,938,763; 5,702,716; 5,744,153; 5,990,194; and 5,324,519. These compositions are administered to the body in a liquid state or, alternatively, as a solution, typically via syringe. Once in the body, the composition coagulates into a solid. One type of polymeric composition includes a nonreactive thermoplastic polymer or copolymer dissolved in a body fluid-dispersible solvent. This polymeric solution is placed into the body where the polymer congeals or precipitatively solidifies upon the dissipation or diffusion of the solvent into the surrounding body tissues. It is expected that these compositions would be as effective as Lupron® Depot, since leuprolide of these compositions is the same as are in the Lupron® Depot and the polymers are similar.
Surprisingly, however, it has been discovered that the liquid polymeric compositions according to the present invention are more effective in delivering leuprolide acetate than Lupron® Depot. Specifically, the testosterone levels obtained with the liquid polymeric compositions of the present invention containing the leuprolide acetate are lower at extended times in dogs compared to Lupron® Depot, and also at the six month point in humans, compared to the value reported in the literature for Lupron® Depot (Sharifi, R., J. Urology, Vol. 143, Jan., 68 (1990)).